The glucocorticoid receptor in mouse fibroblasts and rat thymic lymphocytes is apparently activated and inactivated in the intact cell. When cells are ruptured, specific steroid binding activity is rapidly lost. We have examined this inactivation of specific binding after cell rupture and determined that it is mediated by an enzyme that is not a protease. A portion of the proposed research will focus on the purification and identification of that receptor-inactivating enzymes. As part of this project we will try to obtain reactivation of the receptor in a subcellular system. We have obtained substantial evidence that phospholipid may participate in the steroid receptor complex (Schulte et al. J. Biol. Chem. in press). We hope to purify the receptor by affinity chromatography and determine the sensitivity of the partially purified binding component to inactivation by phospholipase A. If it is inactivated, we will attempt to identify the phospholipid.